180 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



BLOOD-SUCKING INSECTS AS CARRIERS OF HUMAN 



DISEASES. 



BY C. T. BRUES, 

 Bussey Institution, Harvard University. 



I have been much interested in the summary published in the 

 last number of the Proceedings of the Entomological Society 

 of Washington (vol. xiv, pp. 79-81, April-June, 1912), of re- 

 marks by Dr. Frederick Knab relative to the transmission of 

 human diseases by blood-sucking insects. 



He has called attention to the fact that such insects must be 

 rather constant companions of man in order that their po- 

 tential powers to act as vectors may be utilized. On this 

 account it is stated that such insects as Simuliidae, Tabanidse, 

 and sylvan mosquitoes may be eliminated, as they do not 

 feed regularly on human blood, and are active during only a 

 limited season, a condition that would necessitate too great an 

 interval during which no transmission could occur. In addi- 

 tion, it is stated that with insects which do not normally bite 

 man, the chances of such species obtaining parasitic micro- 

 organisms from an infected person and then inoculating a 

 second person are too remote to allow for the perpetuation of 

 the disease. 



These statements hold good for such diseases as yellow 

 fever and malarial fevers so far as we know, since the pathogenic 

 organisms are confined to man and specific mosquitoes in 

 which they undergo a definite life-cycle. 



Two matters have been overlooked, however, which have a 

 very important bearing on certain other insect-borne diseases. 

 In the first place, there is the possibility that some human dis- 

 eases may be common to animals. This has been demon- 

 strated in the case of some infections, and in at least one in- 

 sect-borne disease is known to occur. Thus, with African 

 sleeping sickness, wild antelopes and domestic cattle may act 

 as reservoirs for the trypanosomes that produce the disease 

 and tsetse flies infected from them may spread the disease in 

 man. That many more animal diseases may bear some such 

 relation to man is probable, although present information 

 relates mainly to infections (e. g., anthrax) which are not or- 

 dinarily insect-borne. 



Secondly, the occurrence of chronic carriers must not be 

 overlooked. Such conditions are best known in certain dis- 

 eases such as typhoid fever and diptheria, where blood-suck- 

 ing insects do not ordinarily spread the infection; but the piro- 

 plasma of tick-borne splenetic fever (Texas fever) of cattle is 

 known to persist in chronic cases. That such is commonly 

 true of some human insect-borne diseases is by no means un- 



